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I am using Synergy to connect my desktop (GNU/Linux. connected via cable to router) to my laptop (OSX ElCapitan. connected via WiFi).

It works like a charm if I use the laptop as the server;

From desktop (client):

me@my-desktop ~ $ sudo lsof -i :24800
COMMAND   PID    USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
synergyc 5533      me    6u  IPv4  46314      0t0  TCP 192.168.0.2:38706->192.168.0.3:24800 (ESTABLISHED)

And from laptop (server):

My-MacBook-Pro:~ me$ sudo lsof -i :24800
COMMAND    PID    USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
synergys 17646      me    4u  IPv4 0x728ca44823ae6a59      0t0  TCP *:24800 (LISTEN)
synergys 17646      me   14u  IPv4 0x728ca44822d02fb9      0t0  TCP 192.168.0.3:24800->192.168.0.2:38706 (ESTABLISHED)

But when I switch it around, it wont connect. (In Synergy I get: Connection timed out).

From the desktop (now server):

me@my-desktop ~ $ sudo lsof -i :24800
COMMAND   PID    USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
synergys 5611      me    6u  IPv4  45707      0t0  TCP *:24800 (LISTEN)

And from the laptop (now client):

My-MacBook-Pro:~ me$ sudo lsof -i :24800
COMMAND    PID    USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
synergyc 17662      me    4u  IPv4 0x728ca4482eed3c39      0t0  TCP 192.168.0.3:60629->192.168.0.2:24800 (SYN_SENT)

I imagine this is some kind of network/firewall problem and not a Synergy problem per say.

So how do I fix this issue? What machine is blocking the communication? My understanding is that since my desktop is listening its port has to be open. And my laptop sends a request so where is the communication blocked?

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  • So what's your question? You're probably right, it's a firewall issue.
    – David Schwartz
    Commented Dec 1, 2015 at 19:49
  • Well, how do I fix the issue? Since it is working one of the ways, which machine is blocking? My desktop is listening so the incoming port has to be open, right? And the laptop is sending a request which does not reach the target, or is it the answer from my desktop that's not getting back to my laptop? I will try and clarify in my question.
    – fredrikekre
    Commented Dec 1, 2015 at 20:28
  • Most likely, it's the desktop whose firewall is rejecting the incoming connection attempt from the laptop.
    – David Schwartz
    Commented Dec 1, 2015 at 20:29
  • Even though its status is (LISTEN)?
    – fredrikekre
    Commented Dec 1, 2015 at 20:32
  • What do you mean by "its"? The status of the socket is LISTEN. The problem is with the firewall though, not the socket.
    – David Schwartz
    Commented Dec 1, 2015 at 20:36

1 Answer 1

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The desktop were blocking the request from the laptop. Simply opening the port solved the problem. Wrote the following in the terminal to open the port:

sudo iptables -I INPUT -p tcp --dport 24800 --syn -j ACCEPT
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2
  • thanks i been struggling for two nights .. you are a wizard
    – zguell
    Commented Feb 5, 2020 at 20:19
  • same here got crazy about this and not sure how that hapend
    – open-ecommerce.org
    Commented Oct 27, 2022 at 8:31

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